fSpy importing camera into an existing scene
&quot;It seems relatively easy&quot; indeed, but it helps if you take some time to explore the real power of f-spy.
The first piece of information you need is the lens focal length and camera sensor size used to make the original image. Without it is going to be hard to get accurate placement.
Unfortunately f-spy wrongly labels &quot;focal length&quot; settings for Sensor Size
You might need to refer to a Lens to Field of View calculator (there are many on the internet) to get the field of view for your lens in degrees (not in mm)
The second part of the puzzle is working with real measurements, fSpy will not guess them for you.

Then, manually move the 3 axis tool in f-spy to set the origin and alignment of the scene: the white dot will determine the placement for the &quot;floor&quot; on the blender scene.
Without any real measurements there all you will get from spy is the  field of view on an arbitrary scene with arbitrary scale and relative distances, making it harder for you to approximate existing elements in blender.